对象导论

　　每个对象都提供服务

light　　

on();

off();

bright();

dim();

light是类名，下面部分是方法接口。

对象的向上转型具体实现：

public class shape {
    void erase(){
        
    }
}

public class circle extends shape{
    void erase(){
        System.out.print("this is a circle");
    }
}

public class square extends shape {
    void erase(){
        System.out.print("this is a squara");
    }
}

public class upcasting {
    void dosomething(shape s){
        s.erase();
    }
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        shape c = new circle();
        shape s = new square();
        upcasting up = new upcasting();
        up.dosomething(c);
        up.dosomething(s);
        
    }

}